Electronic fuel injected engines used in motor vehicles typically include a microprocessor based control system. Fuel is metered, or injector activation time is varied, in accordance with various engine parameters detected through sensors. Some of the parameters include engine temperature, mass air flow rate, present vehicle speed, engine RPM, oxygen content in the exhaust, and, most importantly, the position of the butterfly valve or throttle valve that controls air flow into the engine.
Typically the throttle valve rotates from a closed position to an open position in a span of ninety degrees or less. Throttle valve position detection is accomplished by attaching a rotational position sensor to the rotational axis of the throttle valve. The rotational position sensor produces an output voltage signal in accordance with the relative position of the throttle valve. The accuracy and repeatability of the sensor over an extended period of time must not vary significantly. Otherwise, the engine control computer may be required to compensate for drift or variance of the sensor. Software that must compensate for sensor output signal drift can be unduly complex and waste program memory space better used for engine control algorithms. It is preferred that the sensor produce a linear output and that over the life expectancy of the sensor, the output signal versus rotational position vary only an insignificant amount as temperature extremes are encountered.
Installation of a high accuracy sensor in the engine compartment of a motor vehicle is a requirement with regard to the throttle valve sensor. Temperature extremes in the engine compartment typically result in temperature drift of electronic circuits installed therein.
Linear Hall effect devices are simplistic in operation and may be used with non-contact type magnetic coupling rotary sensors to produce a signal corresponding to angular position. A more reliable throttle position sensor that includes non-contact type operation and Hall effect based electronics would satisfy several concerns of automobile manufacturers good signal to noise ratios are achieved and if the temperature drift of the Hall device is compensated through a low component count temperature compensation circuit. Reducing cost and improving long term accuracy and reliability are the foremost concerns in producing a reliable engine compartment sensor.
A rotary sensor that includes improved signal to noise, a linear output signal response, is more economical to produce and is resistant to temperature extremes is needed.